Port fueled engines may have benefits not provided by direct injection engines and vice-versa. For example, direct injection engines may improve engine power output by lowering cylinder charge temperatures, thereby reducing the possibility of engine knock and allowing higher cylinder pressures. But, by combining direct and port injection systems, it may be possible to provide benefits of both port and direct fuel injection. Fuel injected to a port of a cylinder may be injected over a longer engine crankshaft interval than fuel that is directly injected to a cylinder. In particular, fuel injected to a port for a particular combustion event may be injected from a first intake closing event of the cylinder receiving the fuel until a second intake closing event of the cylinder receiving the fuel. On the other hand, directly injected fuel may be injected from about top-dead-center intake stroke to about top-dead-center compression stroke. Thus, fuel directly injected to a cylinder may be injected later in a cylinder cycle and within a shorter crankshaft duration.
Injecting fuel to an engine having both port and directly fuel injectors may be simplified if the engine is operated at constant operating conditions at all times. However, engines may be subject to changes in speed and torque demand during normal driving conditions to provide desired torque. Consequently, desired engine torque for a particular combustion event may change from a time when port fuel injection begins to a time direct fuel injection begins. If a change in engine torque occurs without adjusting the amount of fuel injected to the engine, the engine torque and air-fuel ratio may vary from a desired engine torque and air-fuel ratio, thereby increasing engine emissions. Therefore, it may be desirable to provide a method for injecting fuel to an engine that provides for revising an amount of fuel injected to a cylinder as an estimate of cylinder torque, or alternatively, cylinder air charge, varies during an engine cycle.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine fueling method, comprising: providing a first port fuel injection window defined by a first crankshaft angle and a second crankshaft angle in a cylinder cycle in response to a first port fuel injector pulse width; and providing a second port fuel injection window defined by the first crankshaft angle and a third crankshaft angle in the cylinder cycle in response to a second port fuel injector pulse width.
By providing different duration port fuel injection widows in response to fuel injector pulse widths, it may be possible to provide the technical result of providing a fuel injection process for an engine having port and direct fuel injectors that compensates for changes in engine torque or air flow during a cylinder cycle. In particular, for smaller port fuel injection pulse widths, a port fuel injection window may be shortened so that the port injected fuel amount may be adjusted several times before port fuel injection for a cylinder cycle ceases. Further, the port fuel injection window may be shortened so that port fuel injection ceases before direct fuel injection is scheduled. As a result, the directly injected fuel amount may then be scheduled based on the known amount of port injected fuel and the estimated cylinder air mass. For longer port fuel injection pulse widths, the port fuel injection window may be lengthened, and the amount of port injected fuel is not updated for changes in the estimated cylinder air amount or engine torque. Consequently, the port injected fuel mass may be known before the direct injected fuel is scheduled even as port injected fuel continues to be injected. The directly injected fuel mass is then based on the known port injected fuel mass and an updated cylinder air mass. In this way, it may be possible to deliver an accurate amount of fuel to a cylinder during a cylinder cycle even though an estimate of cylinder air charge or engine torque may change during a cylinder cycle. Further, by permitting longer port fuel injection windows, it may be possible to provide greater amounts of engine torque than would be possible via only directly injecting fuel.
The present description may provide several advantages. For example, the approach may improve engine air-fuel ratio control. Additionally, the approach may provide for increased amounts of engine torque as compared to when fuel is injected via only a single fuel injector. Further, the approach provides for smoothing transitions between shorter port fuel injection windows and larger port injection windows so that the possibility of engine air-fuel ratio disturbances may be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.